1. Field of the Invention
The invention relates to a thin-walled circular-shaped metal structure and a method of fabricating the same, and more particularly to such a metal structure usable as a photosensitive drum or a fixing roller in an electrophotographic printer or copier, and a method of fabricating the same.
2. Description of the Related ART
For instance, in accordance with Japanese Unexamined Patent Publication No. 10-10893, a film of which a photosensitive drum or a fixing drum used in a conventional electrophotographic printer and copier is fabricated is composed generally of organic material such as polyimide or a metal as inorganic material, such as iron, aluminum, stainless steel and nickel.
The above-mentioned film is required to have a thickness in the range of 0.03 to 0.20 mm as a practical thickness. However, such a thickness can be accomplished only by a film composed of polyimide or nickel. For instance, a nickel film having such a thickness can be fabricated by electrocasting.
It is generally said that a fixation section consumes about 80% of power to be totally consumed in an electrophotographic printer or copier. In addition, power consumption depends greatly on a material of which a fixing roller or a fixing film is composed.
For instance, if a fixing roller or film is composed of polyimide, an organic material, having a thermal conductivity 1/510 to 1/40 smaller than a thermal conductivity of the above-mentioned iron, aluminum, stainless steel or nickel, it would be necessary to heat a fixing roller or film much time until the fixing roller or film become workable. A period of time in which a fixing roller or film is heated is a time in which a user has to wait after a printer or copier has been turned on until the printer or copier becomes workable. Since a user usually desires a printer or copier to become workable as soon as possible, a fixing roller or film has to be heated even when the printer or copier is not in use, resulting in an increase in power consumption.
On the other hand, if a fixing roller or film is composed of nickel having a thermal conductivity 210 times greater than that of polyimide, it would be necessary to heat a fixing roller or film less time than a time during which a polyimide film has to be heated, until the fixing roller or film become workable. As a result, it is no longer necessary to heat a fixing roller or film to heat in advance, and hence, a printer or copier including the fixing roller or film composed of nickel becomes workable immediately when the printer or copier is turned on.
As mentioned above, power consumption in a printer or copier can be reduced by using a nickel film as a fixing film. However, a conventional method of fabricating a nickel film is accompanied with problems as follows.
As mentioned earlier, a nickel film having a thickness of 0.03 to 0.20 mm is fabricated by electrocasting. That is, such a nickel film is fabricated by precipitating nickel ions by electrolysis. Hence, the thus fabricated nickel film has such a columnar crystal structure as illustrated in FIG. 7, and resultingly, has a shortcoming that the nickel film is weak to a mechanical repeated stress.
In addition, in accordance with a fatigue test, the nickel film has a lifetime in the range of a couple of tens thousand rotation to a couple of millions rotation. There is much dispersion in a lifetime of a nickel film.
In particular, a nickel film fabricated by electrocasting shows remarkable thermal embrittlement when heated to a temperature over 200 degrees centigrade. Hence, a nickel film fabricated by electrocasting is not suitable as a fixing film.
Though ions can be readily precipitated out of a pure metal by electrocasting, it is almost impossible to precipitate ions out of an alloy such as a stainless steel.
As another method of fabricating a metal cylindrical film, there has been suggested a method including the steps of rounding a thin film having a thickness in the range of 0.03 to 0.20 mm, and welding the thus rounded film into a cylinder-shaped film. According to this method, any metal may be used for fabricating a metal cylindrical film.
However, this method is accompanied with such a problem of shortage in a mechanical strength and non-uniformity in a shape of a cylinder, due to a bead treatment at a welded portion, and further due to a defect in a welded portion with respect to a metal structure. In addition, since a metal cylindrical film is fabricated in the method by splicing thin films to each other, a skill is required and it takes much time to do so, resulting in an increase in cost and absence of mass-productivity. Hence, the method is not put to practical use yet.